1. Field of the Invention
The present invention relates to air intake systems for internal combustion engines and, more particularly, to an air intake system for carburetor-type and fuel-injection-type internal combustion engines featuring a device for controlling the intake air temperature by means of a continuously adjustable air proportioning valve which admits a variable ratio of cold air and preheated air to maintain an optimal air intake temperature under changing ambient temperatures.
2. Description of the Prior Art
Various devices aimed at maintaining an even air intake temperature under changing ambient temperatures, especially low ambient temperatures, are known from the prior art.
One such device is suggested in the German Pat. No. 15 26 662. This device is simple in its configuration and therefore suitable for mass production at low cost. It features a right-angle junction between a cold air intake duct and a warm air intake duct which is controlled by a pivotable inlet flapper. In one extreme position, the flapper closes the cold air intake duct while opening the warm air intake duct and, in the other extreme position, it closes the warm air intake duct while opening the cold air intake duct. A wax thermostat is arranged in the raw air mixing duct downstream of the duct junction and its drive pin is connected to the shaft of the inlet flapper by means of a rod and linkage. As the temperature of the air flowing past the wax thermostat increases, the latter moves the flapper in the direction of closing the warm air intake duct, in opposition to a return spring. The wax thermostat, as a control element, provides adequate adjustment output for this purpose, both in terms of adjustment force and in terms of adjustment stroke.
However, it has been found that the location of the wax thermostat in the raw air mixing duct presents a certain problem, inasmuch as the actual temperature response of the wax thermostat may deviate considerably from the average temperature of the aspirated raw air, the deviation being different under different operating conditions of the internal combustion engine.
This response deviation is due to the fact that, in the area of the wax thermostat, the raw air flow forms distinct strands of warm and cold air which, depending on the amount of air flow passing through the air intake system, impinge on the housing of the wax thermostat in different ways.
Past experience has also shown that these apparent inconsistencies in the thermostat response cannot be sufficiently compensated for by relocating the wax thermostat at a greater distance from the duct junction and by transmitting the displacements of the thermostat pin to the inlet flapper with appropriate mechanical, hydraulic or pneumatic means. On the other hand, it is a fact that the longer transmission path increases the complexity and the cost of the device, while representing an additional potential source of malfunction.
The German Offenlegungsschrift No. 19 26 181 describes a device for controlling the intake air temperature by means of two thermostats which cooperate to adjust a pivotable inlet valve controlling the flow out of oppositely located cold air and warm air inlet ducts into a duct junction. The two thermostats are bimetallic spiral springs. They are arranged in a series-type drive connection which transmits the sum of the thermostat displacements to the pivot shaft of the inlet valve. One thermostat is arranged on the outside of the duct junction, so as to respond to the ambient air temperature, and the other thermostat is arranged near the upstream extremity of the raw air mixing duct.
The purpose of this structure is to provide a compensation for the heat losses which occur, when the raw air flow passes through the cold filter assembly, with the aim of supplying combustion air to the carburetor at a temperature which is as even as possible, independently of the operating condition of the internal combustion engine. However, this objective is attained only to a limited degree, because the air inlet valve does not fully take into account changes which take place in the warm air supply under different engine operating conditions. It follows that the resultant temperature of the mixed raw air is again uneven.
The German Offenlungsschrift No. 27 55 086 discloses a device which uses two wax thermostats in two different versions of the device. The first version features two right-angle junctions, a first one between two intake ducts for warm air and cold air with a pivotable inlet flapper which is controlled by a wax thermostat arranged in the raw air mixing duct, and a second one between the raw air mixing duct downstream of the first duct junction and a second cold air intake duct with a similar inlet flapper which is controlled by the second wax thermostat. The latter is arranged in the second cold air intake duct which thus serves as a bypass inlet.
The second thermostat responds to an elevated ambient temperature by completely closing off the first right-angle junction from the raw air mixing duct, admitting only cold air through the bypass inlet. The response behavior of the first thermostat in the raw air mixing duct is again characterized by deviations which are due to the formation of separate flow strands of cold and warm air in the duct.
The second version of the device disclosed in this publication has a single duct junction with a pivotable inlet flapper which is controlled by two wax thermostats of which one is arranged in the raw air intake duct and the other is arranged in the cold air intake duct. The drive connection between the two wax thermostats and the flapper shaft is of the parallel, lost-motion type, i.e. non-additive. Again, the wax thermostat in the raw air mixing duct is operating under response deviations, due to the large cross section of the mixing duct which permits separate flow strands of different temperatures to flow past the thermostat.
The Austrian Pat. No. 135 591 discloses a T-junction between two axially aligned opposing intake ducts for warm air and cold air, respectively, and a raw air mixing duct, the flows from the two intake ducts being controlled by means of two rotary disc valves which are mounted on a common shaft in the center axis of the two intake ducts. Connected to the axial extremities of this shaft are the ends of two thermostat members in the form of bimetallic spiral springs, one thermostat member being arranged in the cold air intake duct and the other being arranged in the warm air intake duct.
The connection between the valve shaft and the spiral springs may be of the series-type, in which case the displacements of the two thermostat members are added together, or it may be of the parallel-type, in which case the displacements are averaged out. This device has the shortcoming that it does not take into account any differences in the flow rates at which air passes through the two intake ducts, so that uneven temperatures of the mixed raw air are obtained. The axially aligned, opposing configuration of the two intake ducts is difficult to accommodate in an air intake system for an internal combustion engine. The two rotary disc valves provide a relatively small flow cross section in the ducts, and the overall device is complex and therefore costly to manufacture in mass production.